JPS5839427A - Apparatus for molding plastic - Google Patents

Abstract

PURPOSE:To reduce the consumption of electric power, to facilitate the temperature control, and to reduce the cost for manufacturing molds, by forming a hot runner from an electrically conductive pipe with a low heat capacity, and heating the hot runner by electromagnetic induction heating. CONSTITUTION:A gate 1a is provided in a part opposite to a molding part 2a of a fixed mold 1, a gate body 4 is provided for the gate 1a, and the electrically conductive pipe 10 connects the gate body 4 with a nozzle bush 13. An insulating layer 11 of ceramic, asbestos or the like is formed on the outer circumferential surface of the runner pipe 10, and an electromagnetic induction coil 12 is wound around the insulating layer 11, and is connected via a transformer connecting section 16 to a high-frequency oscillating circuit 17 and a temperature controlling system 8. When a synthetic resin is injection molded, the temperature of the runner pipe 10 is controlled by the temperature controlling system 8 so that the resin in the pipe 10 that will be supplied from the nozzle bush 13 is kept in a molten state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a hot runner 1 of a plastic molding apparatus, that is, a hot runner that accommodates resin in a molten state between a melting cylinder and a molding section of a mold.

In plastic molding equipment, there is a part of the runner in the resin passage from the melting cylinder to the molding part of the mold.
In the case of cold runners, this meant that the material had to be crushed and regenerated after molding, and was discarded as is. In order to eliminate this waste, a part of the cold runner is always melted, and most of the injected resin is molded without a part of the cold runner, which is the hot runner molding method. In this method, a sheath heater is installed in the resin passage from the melting cylinder to the molding part of the mold, and the entire mold with a large heat capacity is heated to keep the resin in a part of the runner always in a molten state. According to this method, the runner does not apply any force to the molded product, so there is no wastage of material, and there is no need to separate part of the runner from the molded product, recycle it, or dispose of it, so it is easy to process. Although this method is also advantageous, it has the following disadvantages because the entire large mold is heated.

1) Since the entire mold with a large heat capacity (fixed side mold) must be heated, a large amount of heat is required, and power consumption is large, which is a big problem from the point of view of energy conservation.

2) Since the entire mold with a large heat capacity is heated, it is suitable for cooling the mold in the case of resins that require mold cooling, or in the case of forced cooling of the mold to shorten the molding cycle. It is time consuming and difficult to control the temperature of the mold.

3) The sheathed heater as a heat source is prone to wire breakage, and maintenance is difficult because the mold must be disassembled and the heater replaced each time a wire breaks.

4) Since a mold with a hot runner must be designed and processed, the manufacturing cost of the mold is high.

In view of these drawbacks of hot runners, the present invention provides a new plastic molding device that consumes less power, can easily control temperature, is easy to maintain, and can significantly reduce mold manufacturing costs. The purpose is to

The plastic molding apparatus of the present invention does not use a part of the hot runner as a passage in the mold in the conventional hot runner molding method, but instead uses only the molding part of the mold, and a tubular passage ( This runner pipe is made of a conductive material, its outer periphery is coated with an insulating material such as ceramic or asbestos, and an electromagnetic induction coil is wound on top of this. This system is characterized by generating heat to heat the resin inside the Ranka Vibe and keep it in a molten state.

In other words, the hot runner is made of a tubular runner (part of the runner) made of a conductive material with a small heat capacity, and is heated by electromagnetic induction heating. Responsive heating can be achieved, and when cooling is required, responsive cooling is possible.Furthermore, the production cost is low, and there is no need to disassemble and replace the mold when the wire breaks, as with sheathed heaters. Maintenance is easy.Of course, the design and measurement of the mold becomes easier, and less energy is required for heating, so the economic benefits are extremely large.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a partial sectional view showing a part of a molding apparatus using the runner section of the present invention, and FIG. 2 is an enlarged sectional view of the gate portion thereof.

The stationary mold 1 is provided with a gate 1a at a portion facing the molding part 2a of the movable mold 2, and a ceramic gate having a conductive heating element 3 on the inner wall is provided at the gate 1a. A main body 4 is disposed, and an electromagnetic induction coil 5 is wound around the outer peripheral surface of the gate main body 4. This coil 5 is connected to the left and right gates of the stationary mold 1 by a lead wire 5a so as to be commonly wound in series, and further led to a transformer coupling portion 6 via a lead wire 5b. It is connected to a high frequency oscillator circuit 7 through the circuit, and is supplied with high frequency. This high frequency oscillation circuit 7 is controlled by a temperature control system 8 to perform necessary temperature control.

A runner/cive 10, which is the main component of the present invention, is screwed onto the upper part of the gate body 4 by the male screw 10a of the cive 10 and the female screw 3a of the heating element 3. An insulating layer 11 made of ceramic, asbestos, or the like is formed on the outer peripheral surface of the runner pipe 10, and an electromagnetic induction coil 12 is wound thereon. A part of the runner (eve 10 is made of a conductive material such as iron to generate heat by electromagnetic induction, and in the illustrated embodiment, there are two eaves at the branch point tab so as to supply molten resin from the nozzle bush 13 to the two gate bodies 4. The nozzle bushing 13 has a forked shape.
As is well known, a nozzle for injecting all of the molten resin is pressed into contact with the nozzle fixed at 4. This support stand 14 is preferably formed integrally with the stationary mold l, and firmly supports the entire inlet end 10c of the runner pipe 100 of the nozzle, so as to prevent the pressure contact force of the nozzle from being transmitted to the runner pipe lO. do.

Furthermore, if the runner pipe IO expands and deforms during heating, there is a risk that the relative position between the gate body 4 and the gate portion 1a of the mold 1 may shift, so the runner pipe IO is supported by solid support means such as ceramic. It is necessary to prevent deformation.

The electromagnetic induction coil 12 wound around the outer periphery of the insulating layer 11 coated on the runner pipe IO is connected to the transformer coupling portion 161.
&: is connected to the high frequency oscillation circuit 17 and to the temperature control system 8.

The temperature control system 8 includes the two high frequency oscillation circuits 7.17
i control to make each necessary eve 10 generate heat, and also perform temperature control. That is, the heating element 3 in the gate part is heated when the molten resin in the hot runner is injected into the molding part 2a of the mold, and the resin is injected from the mold part 2a, and when the mold is opened, heating is stopped and the heating element 3 is cooled. The injection of resin from the gate la is stopped. On the other hand, the runner pipe 10 is constantly heated while being controlled at an appropriate temperature to keep the resin inside in a molten state.

In the embodiment described above, electromagnetic induction heating is employed not only in the runner pipe 10 but also in the gate portion, but conventional methods may be used for temperature control or opening/closing of the gate portion. That is, the present invention is characterized in that the hot runner is shaped like a pipe to reduce its heat capacity and to facilitate temperature control, and any structure may be adopted for the gate portion.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view showing one embodiment of the present invention, and FIG. 2 is a partially enlarged sectional view thereof. 1...Fixed side mold 1a...Gate 2
...Movable side mold 2a...Molding part 3.
......Heating body 4... Ceramic gate body 5...
Electromagnetic induction coil 6, 16...Transformer coupling part 7.
17...High frequency oscillation circuit 8...Block temperature control system Figure 1

Claims (1)

[Claims] 1) In plastic molding equipment, the resin passage from the melting cylinder to the molding part of the mold is formed with a conductive tubular runner pipe, and an electromagnetic induction coil is wound around the runner pipe via an insulating layer. Chick forming equipment.